Implant delivery assembly with expandable coupling/decoupling mechanism

ABSTRACT

An occlusive implant delivery assembly includes a rapid response decoupling or detachment mechanism that does not effect significant migration of the implant during release. The assembly includes an occlusive implant device, such as an embolic coil, a pusher or device to carry the implant to the selected location, and an expandable coupling-decoupling mechanism for releasing the implant at the selected site. The mechanical construction provides rapid release times. In addition, the releasing mechanism generally operates without exerting any significant force on the implant, thereby avoiding any significant displacement of the implant during release.

RELATED PATENT APPLICATION

[0001] This application is a continuation of U.S. Ser. No. 08/363,264,filed Dec. 22, 1994, the entirety of which is hereby incorporated byreference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to surgical instruments.More particularly, the invention relates to delivery assemblies fordelivering an occlusive device, such as an embolic coil, to a selectedsite within a mammal using an expandable coupling or decouplingmechanism.

BACKGROUND OF THE INVENTION

[0003] The endovascular treatment of a variety of vascular maladiesthroughout the body is an increasingly more important form of therapy.Catheters have been used to place various treatment materials, devices,and drugs within arteries and veins in the human body. Examples of thesedevices and their use in such treatments are shown in U.S. Pat. Nos.5,234,437 and 5,261,916, in which methods and devices for delivery ofcoils or wires within the human body to sites, such as aneurysms, toocclude those sites are disclosed. Coils, such as those discussed inthese documents as well as in U.S. Pat. No. 4,994,069, may be of aregular or helical configuration or assume a random convolutedconfiguration at the site. The coils normally are made of a radiopaque,biocompatible metal such as platinum, gold, tungsten or alloys of theseand other metals. In treating aneurysms, it is common to place a numberof coils within the aneurysm. The coils occlude the site by posing aphysical barrier to blood flow and by promoting thrombus formation atthe site.

[0004] Coils have typically been placed at the desired site within thevasculature using a catheter and a pusher. The site is first accessed bythe catheter. In treating peripheral or neural conditions requiringocclusion, the sites are accessed with flexible, small diametercatheters such as those shown in U.S. Pat. Nos. 4,739,768 and 4,813,934.The catheter may be guided to the site through the use of guidewires(see U.S. Pat. No. 4,884,579) or by flow-directed means such as balloonsplaced at the distal end of the catheter. Use of guidewires involves theplacement of relatively long, torqueable proximal wire sections withinthe catheter attached to more flexible distal end wire sections designedto be advanced across sharp bends at vessel junctions. The guidewire isvisible using x-ray techniques and allows a catheter to be navigatedthrough extremely tortuous vessels, even those surrounded by soft tissuesuch as the brain.

[0005] Once the site has been reached, the catheter lumen is cleared byremoving the guidewire (if a guidewire has been used), and one or morecoils are placed into the proximal open end of the catheter and advancedthrough the catheter with a pusher. Pushers are wires having distal endsadapted to engage and push the coil through the catheter lumen as apusher itself is advanced through the catheter. Once the coil reachesthe distal end of the catheter, it is discharged from the catheter bythe pusher into the vascular site. However, there are concerns whendischarging the coil from the distal end of the catheter. For example,the plunging action of the pusher and the coil can make it difficult toposition the coil at the site in a controlled manner and with a finedegree of accuracy. Inaccurate placement of the coil can be problematicbecause once the coil has left the catheter, it is difficult toreposition or retrieve the coil.

[0006] Several techniques involving Interlocking Detachable Coils(IDCs), which incorporate mechanical release mechanisms and GuglielmiDetachable Coils (GDCs), which utilize electrolytically actuated releasemechanisms, have been developed to enable more accurate placement ofcoils within a vessel.

[0007] One technique for detaching an embolic coil is shown in U.S. Pat.No. 5,261,916. According to that technique, a coil having an enlargedportion is mated with a pusher having a keyway adapted to receive theenlarged portion of the coil in an interlocking relationship. The jointbetween the pusher and the coil is covered by a coaxial member. Thecoaxial member is movable by sliding the member axially. As the coaxialmember is moved away from the junction where the coil's member engagesthe keyway of the pusher, the coil is freed from the catheter assemblyand the pusher may then be removed.

[0008] Another IDC device for placement of coils is shown in U.S. Pat.No. 5,234,437. This device includes a coil having a helical portion atleast one end and a pusher wire having a distal end that is threadedinside on the helical coil by use of a threaded section on the outsideof the pusher. The device operates by engaging the proximal end of thecoil with a sleeve and unthreading the pusher from the coil. Once thepusher is free, the sleeve may be used to push the coil out into thetargeted treatment area.

[0009] U.S. Pat. No. 5,312,415 discloses the use of a catheter having aconstricted or feathered end to retain a number of embolic coils on aguidewire for precise placement using a pusher sheath.

[0010] Electrolytic coil detachment is disclosed in U.S. Pat. Nos.5,122,136 and 5,354,295. As disclosed in U.S. Pat. No. 5,122,136, thecoil is bonded via a metal-to-metal joint to the distal end of thepusher. The pusher and coil are made of dissimilar metals. Thecoil-carrying pusher is advanced through the catheter to the site and asmall electrical current is passed through the pusher-coil assembly. Thecurrent causes the joint between the pusher and the coil to be severedvia electrolysis. The pusher may then be retracted leaving the detachedcoil at an exact position within the vessel. Since no significantmechanical force is applied to the coil during electrolytic detachment,highly accurate coil placement is readily achieved. In addition, theelectric current may facilitate thrombus formation at the coil site. Theonly perceived disadvantage of this method is that the electrolyticrelease of the coil may require a period of time that may inhibit rapiddetachment of the coil from the pusher.

[0011] Another method of placing an embolic coil is disclosed in U.S.Pat. No. 5,108,407. This patent shows the use of a device in whichembolic coils are separated from the distal end of a catheter by the useof heat-releasable adhesive bonds. The coil adheres to the therapeuticdevice via a mounting connection having a heat sensitive adhesive. Laserenergy is transferred through a fiber optic cable which terminates atthat connector. The connector becomes warm and releases the adhesivebond between the connector and the coil. Among the drawbacks of thissystem is that it involves generally complicated laser opticcomponentry.

[0012] There is a need to provide alternative mechanical mechanisms fordelivering implants, such as embolic coils, that combine accuratepositioning capability with rapid implant decoupling response times.

SUMMARY OF THE INVENTION

[0013] The present invention provides a mechanical occlusive implantdelivery assembly having a rapid response decoupling or detachmentmechanism that does not effect significant migration of the implantduring release. The assembly includes an occlusive implant device, suchas an embolic coil, a pusher or device to carry the implant to theselected location, and an expandable mechanism that is expanded orcontracted to release the implant at the selected site. The inventionadvantageously incorporates a release mechanism that simply involvesunloading a locking force, which is preferably uniformly applied,thereby avoiding the transmission of any significant force to theimplant during release. In addition, the locking members preferably havegenerally, smooth, rounded configurations so that they do not catch anddislodge previously positioned coils upon retraction.

[0014] According to a first embodiment of the invention, the occlusiveimplant delivery assembly includes an occlusive implant; a pusher havinga proximal section and a distal section; a coupling having first andsecond portions, the first portion being coupled to the distal sectionof the pusher and the second portion being coupled to the implant; andan inflatable member having a proximal portion and a distal portion, theproximal portion being coupled to the distal section of the pusher. Atleast a portion of the inflatable member is disposed in the couplingsuch that when inflated, it expands the coupling and decouples thecoupling from either the implant or the pusher. With this arrangement,rapid implant release times can be achieved with minimal, if any, forcebeing applied to the implant. That is, the hydraulic pressure is onlytransmitted to the detachment point or juncture between the inflatablemember and the implant, and not to the implant.

[0015] According to another aspect of this embodiment, the inflatablemember and coupling are configured so that the hydraulic pressuregenerated by the inflatable member is applied uniformly to the innercircumferential surface of the coupling. Thus, any force that may beapplied to the implant in the radial direction is countered by an equal,but opposite force, thereby avoiding implant displacement duringrelease. In the preferred embodiment, the coupling is cylindrical withan essentially uniform radius and the inflatable member is essentiallysymmetrical about its longitudinal axis in the inflated and uninflatedstates.

[0016] According to another embodiment of the invention the implantdelivery assembly comprises an occlusive implant having a tubularportion; a pusher having a proximal section and a distal section; and

[0017] an inflatable member having a first portion coupled to the distalsection of the pusher and a second portion disposed in the tubularportion of the implant such that upon inflation of the inflatable memberthe implant and member tend to separate. More specifically, the coilslides off of the inflatable member. In addition to causing minimal postdelivery migration of the implant, this construction provides anadvantageously simple one-piece decoupling mechanism, which can bereadily manufactured.

[0018] According to another aspect of this embodiment, the inflatablemember and tubular portion also are configured as described above sothat the hydraulic pressure generated by the inflatable member isapplied uniformly to the inner circumferential surface of the tubularportion. In the preferred embodiment, the inner surface of the tubularportion is essentially symmetrical about its longitudinal axis and theinflatable member is essentially symmetrical about its longitudinal axiswhen inflated or deflated to provide an essentially uniformlydistributed force to the inner circumference of the tubular section.

[0019] According to yet a further embodiment of the invention, theimplant delivery assembly comprises an occlusive implant having atubular portion; a pusher having a proximal section and a distalsection; a core member slidably disposed within the pusher and extendinginto the tubular portion; and a locking member releasably coupled to thecoil and core member. With this construction the release mechanism issimply mechanically expanded to interlock the implant to the pusher andrelaxed to release the implant.

[0020] In a first configuration, the locking member comprises anelastomeric ring, such as an O-ring, and the core member includes alocking portion and a tapered portion adjacent thereto. The diameter ofthe core member exceeds the inner diameter of the ring such that whenthe ring is positioned on the locking portion it expands andfrictionally locks the tubular portion thereto. On the other hand, thetapered portion tapers to a diameter that allows the ring to contract.In the preferred embodiment, the tapered portion is less than or equalto the inner diameter of the ring when the ring is in its relaxed state.When the core member is retracted, the tapered portion becomespositioned within the ring and allows the ring to radially contract andrelease the tubular portion and, thus, the implant, as the lockingmember returns to its relaxed state.

[0021] In another configuration, the locking member comprises a flexiblesleeve and the core member extends into the sleeve and is securedthereto. The sleeve is configured so that when axially compressed, itexpands radially against the inner surface of the tubular portion andfrictionally locks the implant thereto. The core member is retracted tocompress the sleeve against a restraint, expand it radially and lock theimplant to the delivery assembly. When it is desired to release theimplant, the core member is advanced to remove the axial compression andradially contract the sleeve.

[0022] These configurations advantageously eliminate the need forauxiliary hydraulics.

[0023] The above is a brief description of some of the features andadvantages of the present invention. Other features, advantages andembodiments of the invention will be apparent to those skilled in theart from the following description, accompanying drawings and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows a catheter apparatus constructed according to ageneral embodiment of the present invention;

[0025]FIG. 2 is an enlarged, fragmentary view of an occlusive implantdelivery assembly, constructed according to the principles of thepresent invention, disposed within a catheter;

[0026]FIG. 3 is a perspective view of the coupling mechanism that formspart of the release mechanism shown in FIG. 2;

[0027]FIG. 4 is an enlarged, fragmentary view of the implant deliveryassembly of FIG. 2 with the implant positioned at a desired location;

[0028]FIG. 5 is a further view of the implant delivery assembly shown inFIG. 4 with the coupling of the release mechanism expanded to unlock andrelease the implant from the pusher;

[0029]FIG. 6 shows the release mechanism deflated and retracted from theimplant location;

[0030]FIG. 7 is an enlarged, fragmentary view of another embodiment ofthe implant delivery system of the present invention with the releasemechanism in a locked state;

[0031]FIG. 8 illustrates the release mechanism of FIG. 7 in an unlockedstate;

[0032]FIG. 9 is a further embodiment of the release mechanism of thepresent invention;

[0033]FIG. 10 is a further view of the release mechanism shown in FIG. 9showing the mechanism actuated to release the coil therefrom;

[0034]FIG. 11 is a further view of the release mechanism shown in FIGS.8 and 9 illustrating the implant fully detached from the mechanism;

[0035]FIG. 12 is an enlarged, fragmentary view of yet another embodimentof the release mechanism of the present invention showing the mechanismin a locked state;

[0036]FIG. 13 is a further view of the release mechanism of FIG. 12illustrating the mechanism in an unlocked configuration;

[0037]FIG. 14 is yet a further embodiment of the release mechanism ofthe present invention illustrating the mechanism in a lockedconfiguration; and

[0038]FIG. 15 is a further view of the release mechanism of FIG. 14showing the mechanism in an unlocked configuration and the implantreleased therefrom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring to the drawings in detail, wherein like numeralsindicate like elements, several embodiments of an occlusive implantdelivery assembly are shown according to the principles of the presentinvention. The various embodiments employ an expandable mechanism, whichis expanded or contracted, to decouple and release the implant at thedesired site. Although variously configured implants can be used inconjunction with the assembly of the present invention, an embolic coiltype implant will be described for purposes of example.

[0040] The operation of the assembly generally comprises the steps of(1) advancing a catheter through a vessel lumen, for example, to thevicinity of the site to be occluded (e.g., an aneurysm, vascularmalformation, or arterial venous fistula), (2) advancing the implantdelivery assembly through and beyond the catheter to the location, and(3) radially expanding or contracting the release mechanism to detachthe implant from the assembly.

[0041] Referring to FIG. 1, a catheter apparatus 2 suitable for guidingthe occlusive implant delivery assembly and providing actuation pressurefor the hydraulically actuated release mechanism embodiments is shown.Catheter apparatus 2 generally includes a catheter 4, syringe 6 andsidearms (adapters) 8A and 8B. Catheter 4 generally comprises anelongate tubular member having proximal and distal end portions 10 and12. The catheter is preferably between about 50-300 cm in length, andtypically between about 60-200 cm in length. The catheter also isdesigned for accessing a vessel site at which, for example,vasoocclusion is desired. For example, the vessel site may be within asmall diameter vessel having 2-5 mm lumen diameter and accessible by wayof a tortuous vessel path which may involve sharp vessel turns andmultiple vessel branches. In that case, the catheter preferably has asmall diameter, flexible construction with a lumen diameter of less thanabout 40 mil, and preferably between about 8-30 mil. Catheters of thistype, which are typically used for accessing deep brain vascular sites,are commercially available.

[0042] The elongated tubular member or catheter 4 is secured at itsproximal end 10 to sidearm 8A, which is of conventional design forintroducing fluids or apparatus into the catheter. The end of proximalsection 32 of pusher 26, which will be described in more detail below,extends through sidearm 8A and is coupled to the distal or downstreamend of sidearm 8B. Sidearm 8B, which is otherwise essentially similar inconstruction to sidearm 8A, can include a tubular extension 14 thatsurrounds a portion of the pusher as shown in FIG. 1. Mandrel 54, 56 or68, which extends through the pusher, as will be discussed below inconnection with FIGS. 9-15, extends through one tube of sidearm 8B. Thedischarge tip of syringe 6, which is used in conjunction with theembodiments shown in FIGS. 2-11 is fluidly coupled to the other tube ofsidearm 8B and, thus, the inner lumen of pusher 26 through which theaforementioned mandrels extend.

[0043] Syringe 6 is of conventional construction and includes acylindrical barrel 18 and a plunger 20 that is reciprocally mountedtherein. A stopcock 22 preferably is provided in the discharge piece ofthe syringe for opening or closing the fluid connection between thesyringe and pusher lumen. Alternatively, the stopcock can be provided ina connector (not shown) that couples the discharge piece of the syringeto sidearm 8B. When the stopcock is in the closed position, thedecoupling or release mechanism of the implant delivery assembly willnot be inadvertently actuated, thereby avoiding wrongly positioning theimplant within the body as a result of such accidental discharge ofliquid from the syringe into the catheter.

[0044] As discussed above, the implant delivery assembly, which isgenerally designated with reference numeral 24 in FIG. 1, is guidedthrough catheter 4 towards the intended vasoocclusion site. Occlusiveimplant delivery assembly 24 generally comprises a pusher or elongatedcarrier member 26, a coil type occlusive implant 28 and a decoupling orrelease mechanism for releasing the implant from the assembly. Althoughcoil 28 is shown in the drawings as a uniform diameter helical coilwire, it may have other configurations. It is important, however, thatthe coil be dimensioned to be able to be advanced through a catheterthat is sized to access the desired site. The coil may be made ofradiopaque, biocompatible metal such as platinum, gold, tungsten,stainless steel or alloys of these metals. Preferably, the coilcomprises platinum, gold, tungsten or alloys of these metals so that itslocation at the site may be readily viewed radiographically.

[0045] For use in occluding peripheral or neural sites, the coils willtypically be made of 0.05 to 0.15 mm diameter platinum wire that iswound to have an inner diameter of 0.15 to 0.96 mm with a minimum pitch(i.e., the windings are close or tight). The length of the wound wire(i.e., the coil) will normally be in the range of 0.5 to 60 cm, andpreferably 0.5 to 40 cm. For wires intended for use in vessels withdiameters of about 2 mm and smaller, the coil has a preferred length ofabout 0.5 to 20 cm. The coil can have any shape. For example, it can beformed so that it takes an essentially linear configuration in which itmay be advanced through the catheter and assume a randomly orientedconfiguration, such as helical, after it is released from the catheterand in a relaxed state as disclosed in U.S. Pat. No. 4,994,069, which ishereby incorporated herein by reference.

[0046] Referring to FIGS. 2-6, a first embodiment of the occlusiveimplant delivery assembly, will be described. The delivery assemblyshown in FIGS. 2-6 generally comprises a pusher or elongated carriermember 26, coil 28 and coupling 30. The pusher preferably has a tubularconstruction to provide a lumen for fluidly coupling a source ofpressurized fluid, such as syringe 6, and an inflatable member utilizedin decoupling the coil from the pusher, as will be described in moredetail below. Pusher 26 also preferably has a proximal section that isrigid enough to facilitate torque transmission to the distal portion ofthe pusher. The distal section of the pusher may be constructed to bemore flexible than the proximal portion to facilitate navigation of thedistal section into very tiny vessels encountered in the brain, forexample.

[0047] In the preferred embodiment, proximal tubular section of pusher26 (designated with reference numeral 32) is a metal tube, preferably astainless steel tube, and the distal section of pusher 26, section 34,comprises a coil 36, which is wrapped in a flexible, elastomeric film 38to fluidly seal the spaces between the coil windings. Film 38 alsooverlaps section 34 to seal the juncture between section 34 an coil 36.Film 38 can be in the form of shrinkwrap and, thus, applied to coil 36and proximal section 34 with conventional shrinkwrap techniques. Coil 36and, thus, distal coiled section 34 is secured to the proximal tubularsection 32 by welding, soldering, brazing, or adhesive.

[0048] Alternatively, a more simple pusher configuration may be used inwhich the pusher comprises a rigid plastic tube which can be ground witha tapered distal section to achieve the desired flexibility. Suitablematerials for this configuration include PEEK and polyimide. The innerdiameter of the distal section in this configuration preferably issignificantly less than the outer diameter of the proximal section towhich the balloon can attached (e.g., glued). In a preferred embodiment,the lumen, which provides for fluid flow between the source ofpressurized fluid and the balloon, has a diameter of about 0.007 inchthroughout its length and the distal section has an outer diameter ofabout 0.014 inch. The outer diameter of the proximal section depends onthe application. For a 3 French catheter, the outer diameter of theproximal section may be about 0.016 to 0.018 inch. Although particularpusher configurations have been described, it should be understood thatother configurations may be used without departing from the scope of theinvention.

[0049] A conventional inflatable balloon 40, having a constructionsimilar to those used in conventional balloon catheters, is secured tothe distal end of coil 36 by adhesive, for example, such that a fluidtight path is formed between the interior of the balloon and the centrallumen of pusher 26, which is formed by proximal and distal sections 32,34 of pusher 26.

[0050] Returning to FIG. 2, balloon 40 extends into tube 42, which isalso secured to implant coil 28 by welding, soldering, brazing oradhesive. As shown in FIG. 2, coupling 30 comprises a tubular member orsplit tube having slots formed in the axial direction and which openinto the end of the tube that is directly coupled to the distal portionof pusher coil 38. The tube to pusher coupling can be accomplished by apressure fit, welding, soldering, brazing or adhesive. Slots 42 formmultiple segments 44 in tubular coupling 30 and facilitate displacementof those segments to effect release of the coil implant from the pusher,as will be described in more detail below. Although a two slotconfiguration is shown, other multiples of slots can be used tofacilitate displacement of the proximal portion of the coupling as wellas other conventional jaw or latch clamping configurations.

[0051] Tubular coupling 30 can be made from platinum, stainless steel orplastic that is biocompatible with the environment in which the couplingwill be placed. The coupling 30 preferably also has a very thin wall ofabout 0.001 to 0.0003 inches.

[0052] The implant delivery assembly of FIGS. 2-6 will be furtherdescribed by way of the following operative example which is providedmerely for exemplary purposes and is not intended to limit the inventionto a particular application.

[0053] A catheter is inserted through the vessel lumen to the site to beoccluded (e.g., an aneurysm, vascular malformation, or arteriovenousfistula. Conventional catheter insertion and navigational proceduresinvolving guidewire and/or flow-directed means may be used to access thesite with the catheter. Thus, although not shown, catheter 4 may includea guidewire useable therewith to guide the distal end of the cathetertoward the desired or selected occlusion site. Guidewires of this typeare commercially available, and generally include an elongate wirehaving a tapered, wire-wound distal end region which is adapted to beadvanced through a tortuous vessel path, with the catheter being movedaxially along the advanced guidewire.

[0054] Once the distal end of the catheter is positioned at the selectedsite (its location may be determined by a coating at the distal end ofthe catheter with a radiopaque material or otherwise affixing such amaterial to the distal end of the catheter or incorporating such amaterial into the distal end of the catheter), the catheter is cleared.For example, if a guidewire has been used to position the catheter, itis withdrawn from within the catheter.

[0055] Then, the implant delivery assembly, as shown in FIG. 2, isintroduced into the proximal end portion of catheter 4, and advancedtoward the distal end portion of catheter 4. The proximal end of pusher26 is manipulated via sidearm 8B, to which it is attached, so thatcoupling 30 and coil implant 28 extend beyond the distal end of thecatheter with coupling 30 free of the catheter and the coil positionedexactly at the desired site (FIG. 4). Stopcock 22 is then placed in anopen position and the plunger of syringe 6 advanced to inflate balloon40 as shown in FIG. 5. As balloon 40 is inflated, it further opens splittube or coupling 30, i.e., segments 44 are displaced radially outward todecouple coupling 30 and coil 28 from pusher 26 without transmitting anysignificant force to coil 28. The balloon is then deflated by retractingthe plunger in syringe 6, thereby releasing coupling 30 from balloon 40so that the pusher can be retracted without altering the position ofcoil 28. After the desired number of coils have been placed at the site,the catheter is withdrawn from the vessel.

[0056] Referring to FIGS. 7 and 8, a further embodiment of the releaseor decoupling mechanism is shown similar to that shown in FIGS. 2-6, butin which coupling 30′ has its proximal portion fixedly secured to thedistal end of coiled portion 34. In addition, coupling 30′ includes endwalls 48 at its distal end for overlapping end piece or cap 50 providedat the proximal end of coil implant 28′. That is the end walls, whichgenerally form jaws, releasably secure coil 28′ to coupling 30′ and,thus, releasably secure coil 28′ to pusher 26. Coupling 30′ also differsfrom coupling 30 in that slots 42′ are formed in the distal portion ofthe coupling. Once the coil implant is positioned at the desiredlocation, fluid is introduced through the hollow pusher member and intoballoon 40, as described above, to displace segments 44′ radiallyoutward and release coil 28′ from coupling 30′ (FIG. 8). The balloon canthen be deflated and the pusher retracted. With this configuration, thecoupling is advantageously withdrawn with the pusher.

[0057] Referring to FIGS. 9-11, a further embodiment of the invention isshown. This embodiment essentially differs from those described above inthat the release or decoupling mechanism simply comprises a balloon. Theballoon extends from the pusher with its proximal portion close fitwithin coil 28. When it is desired to deploy the coil, the balloon isinflated, and as the balloon expands, the coil slides off the end of theballoon as will be described in more detail below.

[0058] The decoupling mechanism of FIGS. 9-11 comprises a balloon 40′having its open end secured to the distal coiled section 34 of pusher26, for example, by adhesive. Balloon 40′ is packed into the proximalportion of coil 28 such that the balloon frictionally engages the innersurface of coil 28 and secures the coil to the balloon. To enhance thesecurement between the coil and balloon, the balloon is constructed suchthat, when in the deflated state, the balloon has a plurality ofcircumferentially extending ribs 52, which preferably are configured tohave a pitch corresponding to that of the coil so that the ribs cansnugly fit between the windings of the coil. The ribs can be formed byplacing a mandrel into the balloon, wrapping a thread around the balloonin the regions where the ribs are desired to be located, and thendipping the balloon, mandrel and thread assembly in a reservoir ofelastomeric material, such as silicon, to form an outer ribbedelastomeric coating for the balloon.

[0059] The decoupling mechanism of the embodiment illustrated in FIGS.9-11 also preferably includes a mandrel 54 which extends from outsidesidearm 8B through catheter 12 via the interior lumen of pusher 26 andinto balloon 40′. Mandrel 52 facilitates inserting balloon 40′ withincoil 28 and preferably is sized to force the outer wall of the balloonagainst the inner circumferential surface of coil 28 to enhance theinterlocking connection between the coil and balloon.

[0060] In operation, the pusher and the mandrel are advanced throughcatheter 4 until coil 28 is positioned at the desired location (FIG. 9).The mandrel is then retracted or withdrawn from the balloon and thesyringe actuated to inflate the balloon 40′ as described above (FIG.10). In this case, it is important that mandrel 54 is sized so that whenplaced in the pusher lumen, sufficient space between the mandrel and theinner surface of the proximal and distal sections 32, 34 of pusher 26 isformed. In this manner, the interior of balloon 40′ can be fluidlycoupled to the syringe 6 when stopcock 22 is in the open position andthe mandrel is in the pusher. As the balloon inflates and stretches, theribs generally flatten and the proximal end of coil 28 slides off thedistal end portion of balloon 40′. In order to avoid axial displacementof the coil, the balloon can be retracted as it is inflated.Alternatively, the end of the balloon can be positioned where theproximal end of the coil is desired to be finally located. As theballoon inflates, the proximal end of the coil will ultimately belocated at the distal end of the balloon. The balloon position can bedetermined by conventional means such as radiographic techniques. Thepusher can then be retracted as shown in FIG. 11 and the balloondeflated. The procedure is repeated if the delivery of additional coilsis desired.

[0061] Referring to FIGS. 12-15, further embodiments of the inventionare shown in which the release or decoupling mechanism comprises amechanically expandable or locking member rather than a fluidlyinflatable/expandable balloon. The expandable locking member fits withinthe proximal end of the coil and is radially expanded to grip the innercircumferential surface of the coil. When the expandable member isreturned to a generally relaxed state so that its diameter decreases,the coil is released.

[0062] The decoupling mechanism shown in FIGS. 12 and 13 generallycomprises core wire or actuating member 56 and an elastomeric ring orlocking member 60, such as an O-ring, which is slidably mounted on corewire 56. Core wire or mandrel 56 includes a proximal locking portion 62,which preferably has a generally uniform diameter, and a distal taperedor unlocking portion. More specifically, the diameter of the core wirelocking portion exceeds the inner diameter of the ring such that whenthe ring is positioned on the locking portion it expands against theinner circumferential surface of coil 28 and frictionally locks the coilthereto (FIG. 12). On the other hand, the tapered portion tapers to adiameter that allows the ring to radially contract and release the coil.In the preferred embodiment, the tapered portion tapers to a diameterthat is less than or equal to the inner diameter of the ring when thering is in its relaxed state. When the core wire is retracted, thetapered portion becomes positioned within the ring and allows the ringto radially contract and release the coil as it returns to its relaxedstate (FIG. 13). Core wire 56 can be ground to the desired shape as isconventional in the art.

[0063] In addition, the distal portion of actuating member 56 includes astop member 66 to ensure that the elastomeric ring 60 does not becomedetached from the actuating member. Otherwise the ring would become freeto migrate in the blood stream, which could result in an embolism. Adisc 58 optionally may be secured to the distal end of coil 36 bywelding, soldering, brazing or adhesive to simplify retraction of thepusher as will be discussed in more detail below.

[0064] In operation, ring 60 is positioned on the locking portion ofcore wire 56 between the core wire and coil 28. Then, the pusher andcore wire are both advanced through catheter 4 so that coil 28eventually extends beyond the catheter and is positioned at the desiredlocation (FIG. 12). Once coil 28 is so positioned, core wire 56 isslowly retracted, causing the tapered distal portion 54 to slide withinthe opening of ring 60, thereby allowing the ring to return to itsrelaxed, unexpanded state. In this state, the ring diameter issignificantly less than the inner diameter of coil 28 to facilitaterapid coil release. As the core wire is further retracted, stop member66, which has a larger diameter than the inner diameter of ring 60,catches the ring and carries it as the core wire is completely withdrawnfrom coil 28 (FIG. 13). When disc 58 is incorporated, the entire pusher26 can be withdrawn by merely retracting actuating member 56 as stopmember 66 acts on coil 36 through ring 60 and disc 58 as is apparentfrom the drawings.

[0065] Referring to FIGS. 14 and 15, a further embodiment of the releaseor decoupling mechanism is shown. The decoupling mechanism illustratedin these figures generally comprises a core wire or actuating member 68,disc or retaining member 70 and sleeve or locking member 72. Sleeve 72is compressed to expand it in the radial direction and interlock thecoil to the pusher assembly (FIG. 14). Once in place, it is extended torelease the coil therefrom (FIG. 15).

[0066] Core wire 68 extends from sidearm 8B as shown in FIG. 1. Thedistal end portion of core wire 68, preferably is secured to the distalend of sleeve 72 so that when the core wire 68 is retracted, sleeve 72is compressed in the axial direction against disc 70 as shown in FIG.14. Sleeve 72 preferably is of a material that, upon compression in theaxial direction, will expand radially to interlock with coil 28.Accordingly, sleeve 72 can comprise fabric and, preferably, comprisesbraided material in which the degree of radial expansion generallydepends upon the pitch of the braiding.

[0067] The actuator is initially positioned as shown in FIG. 14 with theopen end of sleeve 72 compressed against disc 70. The coil is releasedfrom the pusher assembly by simply advancing the core wire 68 as shownin FIG. 15 while maintaining pusher 26 is a fixed position. Then, pusher26 and core wire 68 are concurrently retracted so as to maintain sleeve72 in its extended position, while withdrawing sleeve 72 from coil 28without placing any significant mechanical force on the coil in eitherthe radial or axial direction.

[0068] The above is a detailed description of several embodiments of theinvention. It is recognized that departures from the disclosedembodiments may be made within the scope of the invention and thatobvious modifications will occur to a person skilled in the art. Thefull scope of the invention is set out in the claims that follow andtheir equivalents. Accordingly, the claims and specification should notbe construed to unduly narrow the full scope of protection to which theinvention is entitled.

What is claimed is:
 1. An occlusive implant delivery assembly foroccluding a site in a mammal, said assembly comprising: an occlusiveimplant having a tubular portion; a pusher having a distal section; andan extendable member coupled to said distal section of the pusher andfrictionally held in said tubular portion when not extended, such thatduring extension of said extendable member, said implant separates fromsaid pusher, said extendable member further having a plurality of ribsthat extend radially outward and engage said tubular portion when saidextendable member is not extended.
 2. The assembly of claim 1 , whereinsaid ribs further extend in a circumferential direction.
 3. The assemblyof claim 2 , wherein said implant comprises a coil having multiple turnsand selected ones of said ribs extend between selected ones of saidturns.
 4. The assembly of claim 3 , further including a core memberpositioned inside said extendable member, said core member being sizedto urge said extendable member against said tubular portion.
 5. Theassembly of claim 3 , further including a core member positioned insidesaid extendable member, extension of said core member mediatingextension of said extendable member.
 6. An occlusive implant deliveryassembly for occluding a site in a mammal, said assembly comprising: anocclusive implant having a tubular portion; a pusher having a distalsection; an extendable member coupled to said distal section of thepusher and frictionally held in said tubular portion when not extendedsuch that during extension of said extendable member, said implantseparates from said pusher; and a core member positioned within saidextendable member.
 7. The assembly of claim 6 , wherein said core memberis sized to urge said extendable member against said tubular portion. 8.The assembly of claim 6 , wherein extension of said core member mediatesextension of said extendable member.
 9. An occlusive implant deliveryassembly for occluding a site in a mammal, said assembly comprising: anocclusive implant having a tubular portion, a pusher having a distalsection; a retractable core member slidably disposed within said pusherand extending into said tubular portion; and a locking member releasablycoupled to the interior of said tubular portion; where said core memberis slidably engageable to said locking member; where said pusher isengageable with said occlusive implant and allows delivery of saidimplant through a delivery sheath and into said site when said coremember is extended and engaged with said locking member, whereby duringretraction of said core member, said locking member uncouples from saidtubular portion and said implant uncouples from said pusher.
 10. Theassembly of claim 9 wherein said implant comprises a coil.
 11. Theassembly of claim 9 wherein said locking member comprises an elastomericring and said core member extends into said ring, said core memberincluding a locking portion having a diameter that exceeds the innerdiameter of the ring when the ring is in a relaxed state.
 12. Theassembly of claim 9 wherein said core member has a proximal end portion,a distal end portion, and a stop member positioned along said distal endportion, said proximal end portion having a diameter greater than theinner diameter of said ring when in a relaxed state.
 13. The assembly ofclaim 1 wherein said tubular portion of said occlusive implant definesan interior lumen.
 14. The assembly of claim 6 wherein said tubularportion of said occlusive implant defines an interior lumen.
 15. Theassembly of claim 9 wherein said tubular portion of said occlusiveimplant defines an interior lumen.
 16. An occlusive implant deliveryassembly for occluding a site in a mammal, said assembly comprising: anocclusive implant having a tubular portion defining an interior lumen,and a pusher having a radially expandable distal section, wherein saiddistal section of said pusher is engageable with said lumen of saidimplant.
 17. The assembly of claim 16 wherein said implant is a coil.18. A method for delivering an occlusive implant comprising the stepsof: a. introducing an assembly comprising i. an occlusive implant, ii. apusher having a distal section, and iii. an extendable member coupled tosaid distal section of the pusher for separating said implant from saidpusher, into a mammalian lumen, and b. delivering the occlusive implantto a selected site by extending said member so to separate said implantfrom said pusher.
 19. The method of claim 18 wherein the extendablemember is an inflatable balloon and said delivery of said occlusiveimplant to a selected site is accomplished by inflating said balloon soto separate said implant from said pusher.
 20. The method of claim 18wherein said assembly additionally comprises a core member that extendswithin said extendable member.